This invention relates to a device for testing the condition of the glass rim surrounding the apertures of bottles where the bottles are capped or otherwise sealed. Reliable detection of flaws in the sealing surface of bottle apertures is one of the greatest problems in the field of bottle inspection. On one hand, even the smallest cracks and chips or other defects which could impair tight seating and sealing of the bottle closure must be reliably detected. On the other hand, testing must not be adversely affected by differences in material, or by the shape of the bottles, or by bubbles below the sealing surface, or by different relative positions between the bottle aperture and the test device. Moreover, there should be no erroneous rejection of the bottles that have a good sealing surface around the aperture. Finally, the testing device should be simple in construction, reliable in operation, and be able to test the condition of the body of the bottle and, particularly, the rim around the sealing aperture at rates of 40,000 bottles per hour or more in a single inspection machine. Simultaneous fulfillment of all of these requirements was not possible before the present invention was made.
There is a known bottle aperture rim condition tester in which there is a mirror aligned with a rotor shaft, said mirror projecting a beam of light from a source of light also lying in the rotor shaft, slantingly out from above in a radial direction onto the rim or sealing surface of the bottle aperture (German Laid Open specification No. 24 11 723). From there, the beam is reflected essentially outwardly to a semiconductor or photoelectric detector such as a solar cell. The inspection field on the aperture rim that is illuminated by the light transmitting mirror is developed approximately rectangularly and rotates with the rotor. As it is sometimes wider than the aperture or sealing surface, respectively, it may be moved somewhat forward during testing, as this is necessary for the attainment of high yields. In this known device, the beam of light on the aperture of the single test channel engaging the entire aperture is scattered from any smooth and regular zone on account of the curvatures of the sealing surface so that the effective surface of the light detector must be very large. This leads to the fact that even the light reflected from a damaged point or zone around the aperture encounters the light detector to some extent, and therefore, reduction of light intensity upon scanning of a damaged zone is often very slight and sometimes is not actually detectable. The ability of this known device to detect points of damage of all types is therefore insufficient.
There is another known device for testing bottle apertures comprising a rotor rotating concentrially to the bottle axis. Several cooperating pairs of light transmitters and light receivers or detectors are arranged on the rotor and these travel over a determined annularly shaped partial area of the bottle aperture or sealing surface, respectively. This device is described in U.S. Pat. No. 3,349,906. The sensitivity of the patented apparatus, because of utilizing a plurality of test channels, should be quite high. However, a disadvantage is that there is a strong influence on the test results by deviations of the aperture position from an ideal position and from the contour of the bottle aperture rims differing from an ideal form. These deviations lead to frequent rejection of flawless bottles. The complicated construction and cumbersome selection of a rotor with its plurality of light-receivers and the corresponding problematical connection of the receiver with the stationary readout device is another unfavorable characteristic.